The role of desiccated thyroid and potassium iodide in the cholesterol-induced atherosclerosis of the chicken

Animal models for the atherosclerosis research: a review

Atherosclerosis is a leading cause of death worldwide, and its mechanisms are still unclear. However, various animal models have significantly advanced our understanding of the mechanisms involved in atherosclerosis and have allowed the evaluation of therapeutic options. The aim of this paper is to review those animal models (i.e., rabbits, mice, rats, guinea pigs, hamsters, avian, carnivores, swine, and, non-human primates) that have been used to study atherosclerosis. Though there is no single perfect animal model that completely replicates the stages of human atherosclerosis, cholesterol feeding and mechanical endothelial injury are two common features shared by most models of atherosclerosis. Further, with the development of genetically modified animals, these models are significantly broadening our understanding of the pathogenesis of atherosclerosis.

Plasma total homocysteine levels during short-term iatrogenic hypothyroidism

Hypothyroidism is associated with increased cardiovascular morbidity, which cannot be fully explained by the atherogenic lipid profile observed in these patients. We have previously found elevated levels of the cardiovascular risk factor, plasma total homocysteine (tHcy), in hypothyroidism. We conducted a longitudinal study on 17 patients who had undergone total thyroidectomy for thyroid cancer. During 6 weeks of discontinued T4 substitution before radioscintigraphy (phase I), they attained a hypothyroid state, which was reversed by resupplementation (phase II). Plasma tHcy, serum creatinine, serum and red blood cell folate, serum cobalamin, and serum cholesterol were determined at 2-week intervals throughout phases I and II. There was a progressive and parallel increase in tHcy (mean, 27%), serum creatinine (37%), and serum cholesterol (100%) during phase I, and these values returned to the original level within 4-6 weeks after reinitiating T4 therapy. Serum and red blood cell folate levels showed only minor, but statistically significant, changes. In a bivariate model, serum creatinine and serum cholesterol were strongly associated with the changes observed in tHcy during short term hypothyroidism. In conclusion, we found a transient increase in both plasma tHcy and serum cholesterol during short term iatrogenic hypothyroidism, and the tHcy response is probably mainly explained by concurrent changes in renal function. The increase in both plasma tHcy and serum cholesterol may confer increased cardiovascular risk in hypothyroid patients.

Further Observations on the Effects of Thyroid Hormone Preparations on Cholesterolemia and Atherogenesis in Cholesterol-Fed Cockerels

Administration of large doses of thyroid hormone preparations (desiccated thyroid powder, thyroxine, triiodothyronine, diiodotyrosine) to cholesterol-fed chicks was associated with decreased rate of weight gain and partial inhibition of hypercholesterolemia. Consistent, definitive inhibition of aorta and coronary atherogenesis was not observed, despite partial suppression of hypercholesterolemia. Potassium iodide and thyroid-stimulating hormone of the anterior pituitary were essentially without effect.

Rate of cholesterol synthesis in hypo- and hyperthyroid rats

The rate of cholesterol synthesis, measured by the rate of incorporation of tritium from body water into the cholesterol molecule, was found to be greater than normal in the hyperthyroid rat and below normal in the hypo-thyroid rat.

Mechanism of Iodide Action on Cholesterol Metabolism

Iodide retards or prevents hypercholesterolemia and the development of experimental atherosclerosis in rabbits. "Protection" is estimated from reduction of plasma and/or hepatic cholesterol. Small doses of iodide do not "protect." Iodide in large doses prevents the hypercholesterolemia resulting from exogenous cholesterol and reduces hepatic cholesterol. This effect is independent of the thyroid gland and is not related to "thyroxin-like" plasma iodine. The influence of iodide on cholesterol metabolism seems to be related to the presence of a butanol-insoluble protein-bound iodine compound in the plasma.